Mitt Romney's top economic adviser said Sunday that former Treasury Secretary Timothy Geithner is mistaken or just plain lying about a conversation the two had about tax increases during the 2012 presidential campaign.

In his new memoir to be released on Monday, Geithner says R. Glenn Hubbard told him he and Romney favored raising taxes, but couldn't admit it yet.

According to Politico, which obtained an early copy of the book, Geithner says Hubbard complained to him because the Obama administration was not backing the Simpson-Bowles deficit reduction plan.

"When you guys are willing to raise taxes, we can talk about Simpson-Bowles," Geithner says he responded to Hubbard.

"Well, of course we have to raise taxes," Geithner writes that Hubbard responded. "We just can’t say that now."

That isn't how Hubbard remembers the conversation.

"I was asking him something like, how can Romney's plan be off base because it's essentially the Bowles-Simpson structure and Bowles-Simpson actually raises revenue," Hubbard told Politico. "But I wasn’t suggesting that we're trying to raise taxes."

Geithner, who served as Treasury secretary during Obama's first term, didn't respond to Politico for the story.

The statement Geithner attributes to Hubbard is in stark contrast with the Romney campaign's stance as well as Hubbard's past.

In his runs for president in 2008 and 2012, Romney signed Americans for Tax Reform’s pledge not to raise taxes under any circumstances if he were elected.

Hubbard helped pass the 2003 tax cuts when he was head of President George W. Bush's Council of Economic Advisers and has long been opposed to raising marginal tax rates.

He has said that raising taxes could be part of a solution in lowering the country's debt and deficits, he said that would only be necessary under a president such as Obama.

He believes a Romney administration would have cut spending and therefore would not have needed to raise taxes. His concession for an Obama administration is simply a matter of math, he said.

"We believed that with our numbers, we would not have to [raise taxes]," Hubbard told Politico. "It's a misunderstanding or either that, he's just lying. But it's not true."

Hubbard also told Politico he got a laugh out of other portions he has read from the book.

"I saw some of the excerpts about housing and I must say I split my side in laughter because Tim Geithner personally and actively opposed mortgage refinancing, constantly," he told the website. "And now he's claiming this would have been a great idea in the country. I don't know how much more ingenuous that is in the book, but that was just a real laugher."

Hubbard is currently dean of the Columbia Business School and was Deputy Assistant Secretary at the Treasury Department under President George H.W. Bush.

He was seen as a possible Federal Reserve chairman during George W. Bush's administration, but the job eventually went to Ben Bernanke. Had Romney won the presidency, he was expected to have been named to that job or Treasury secretary.

Mitt Romney's top economic adviser said Sunday that former Treasury Secretary Timothy Geithner is mistaken or just plain lying about a conversation the two had about tax increases during the 2012 presidential campaign.